Comparison of dumbell-based theory and experiment for a dilute polymer solution in a corotating two-roll mill

The Chilcott-Rallison FENE dumbbell model is used to solve for the polymer and flowfield response in transient startup flow of a dilute solution in a corotating two-roll mill. These predictions are then compared to experiment al results obtained in an identical geometry using a high molecular weight dilute (c/c* similar to 0.1) polystyrene solution. As predicted by the dumb bell model, the experiments indicate a substantial coupling between the pol ymer deformation and changes to the Newtonian flowfield. As the polymer str etches, the experimentally measured shear rate decreases as does the Bow-ty pe parameter. However, dumbbell model parameters based upon an isolated cha in do not result in FENE model predictions quantitatively similar to the ex perimental results. Based upon steady-state birefringence values for the sa me dilute solution in an extension dominated Bow at large strain rates, it appears that chain-chain interactions restrict the maximum attainable polym er deformation. Further calculations incorporating this concept, via a redu ced value of the extensibility parameter L, result in much better agreement with experimental results. (C) 1999 The society of Rheology. [S0148-6055(9 9)01401-7].